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Write a C program to reverse a string
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There are a number of ways one can reverse strings. Here are a few of them. These should be enough to impress the interviewer! The methods span from recursive to non-recursive (iterative).
Also note that there is a similar question about reversing the words in a sentence, but still keeping the words in place. That is
I am a good boy
would become
boy good a am I
This is dealt with in another question. Here I only concentrate on reversing strings. That is
I am a good boy
would become
yob doog a ma I
Here are some sample C programs to do the same
Method1 (Recursive)
#include <stdio.h>
static char str[]="STRING TO REVERSE";
int main(int argc, char *argv)
{
printf("\nOriginal string : [%s]", str);
// Call the recursion function
reverse(0);
printf("\nReversed string : [%s]", str);
return(0);
}
int reverse(int pos)
{
// Here I am calculating strlen(str) everytime.
// This can be avoided by doing this computation
// earlier and storing it somewhere for later use.
if(pos<(strlen(str)/2))
{
char ch;
// Swap str[pos] and str[strlen(str)-pos-1]
ch = str[pos];
str[pos]=str[strlen(str)-pos-1];
str[strlen(str)-pos-1]=ch;
// Now recurse!
reverse(pos+1);
}
}
Method2
#include <stdio.h>
#include <malloc.h>
#include <string.h>
void ReverseStr ( char *buff, int start, int end )
{
char tmp ;
if ( start >= end )
{
printf ( "\n%s\n", buff );
return;
}
tmp = *(buff + start);
*(buff + start) = *(buff + end);
*(buff + end) = tmp ;
ReverseStr (buff, ++start, --end );
}
int main()
{
char buffer[]="This is Test";
ReverseStr(buffer,0,strlen(buffer)-1);
return 0;
}
Method3
public static String reverse(String s)
{
int N = s.length();
if (N <= 1) return s;
String left = s.substring(0, N/2);
String right = s.substring(N/2, N);
return reverse(right) + reverse(left);
}
Method4
for(int i = 0, j = reversed.Length - 1; i < j; i++, j--)
{
char temp = reversed[i];
reversed[i] = reversed[j];
reversed[j] = temp;
}
return new String(reversed);
Method5
public static String reverse(String s)
{
int N = s.length();
String reverse = "";
for (int i = 0; i < N; i++)
reverse = s.charAt(i) + reverse;
return reverse;
}
Method6
public static String reverse(String s)
{
int N = s.length();
char[] a = new char[N];
for (int i = 0; i < N; i++)
a[i] = s.charAt(N-i-1);
String reverse = new String(a);
return reverse;
}
Isn't that enough?
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Last updated:
November 3, 2005
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